The present invention relates generally to devices for detecting very small magnetic fields, and more particularly, to devices for detecting such small magnetic fields by means of amplitude mode sensing.
Magnetic field sensors may be utilized in a variety of applications such as sensing the earth's magnetic field, in warfare sensing applications, and in Geophysical earth exploration. Of particular interest, is the applicability of these devices for use in anti-submarine or anti-ship warfare. Typically, the magnetic fields set up by the metallic structure of moving ships or submarines is quite small, on the order of 10.sup.-7 gauss.
The first optical fiber magnetic field sensor was recently demonstrated at the Naval Research Laboratory. (See the article "Optical Fiber Magnetic Field Sensors" by A. Dandridge, A. Tveten. G. Sigel, E. West and T. Giallorenzi, Electronics Letters, May 1980.) This optical fiber magnetic field sensor had a single mode fiber interferometer configuration. Although the use of an interferometer provides for extremely sensitive field sensing capabilities, the use of interferometric structure to measure induced phase shifts in the fiber leads to a complicated device structure which taxes the state of the art in optical componentry.